In optical semiconductor devices including photocouplers and photorelays, a structure has been used in which a light-emitting element and a light-receiving element are respectively mounted on lead frames and in which the light-emitting element and the light-receiving element are sealed in the state where the light-emitting element and the light-receiving element are placed to face each other (e.g., refer to Japanese Unexamined Patent Publication No. Hei 6(1994)-224245).
FIG. 8 shows a known optical semiconductor device by taking as an example a photocoupler having a double sealed structure. As shown in FIG. 8, a light-emitting element 23 and a light-receiving element 24 are respectively mounted on lead frames 21a and 21b, and light-emitting element 23 and light-receiving element 24 are placed to face each other. These elements are primarily sealed with optically transparent resin 25, and secondarily sealed with light-blocking resin 26.
Such a photocoupler is formed as follows. As shown in FIG. 9, light-emitting element 23 and light-receiving element 24 are mounted on lead frames 21a and 21b, respectively. Then, as shown in FIG. 10, light-emitting element 23 and light-receiving element 24 are placed in the state where they face each other.
As shown in FIG. 11, these are primarily sealed with optically transparent resin 25, thus forming a light channel. Then, as shown in FIG. 12, the elements are secondarily sealed with light-blocking resin 26 in order to block light and protect the elements. Lead frames 21a and 21b are formed, thus forming the photocoupler shown in FIG. 8.
In recent years, with the trend toward higher performance of semiconductor devices and the improvement of packaging density, it has been strongly demanded that optical semiconductor devices be miniaturized. However, as described above, in a known optical semiconductor device, secondary sealing is performed in such a manner that the respective lead frames on the light-emitting and light-receiving sides, which face each other, are covered.
It is necessary to ensure certain degrees of thicknesses of secondary sealing resin on these lead frames. It is difficult to reduce the lead frames themselves, which occupy certain volumes. Accordingly, there has been a limit to miniaturization.